Accident Models for Two-Lane Rural Roads: Segment and Intersections
3. Data Collection
How Data were Collected
Data were extracted from HSIS data files for Minnesota and Washington, from photologs for Minnesota and videotapes for Washington, and from construction plans at the Minnesota Department of Transportation. In addition, weather data for the state of Minnesota were acquired from the Midwest Climate Center. A number of small-scale investigations were also done that made use of other data provided by personnel at the respective Departments of Transportation.
HSIS data are stored in SAS databases. The needed data elements were extracted and assembled into SAS data sets representing the study populations with identifiers for each population bin. Random numbers were used to prepare SAS data sets representing the study samples (with the exception of the Washington intersections). Other sample data were recorded manually on specially prepared data sheets from photologs, videotapes, and plans. These were entered into SAS data sets that were merged with the HSIS data to obtain the full sample data sets.
Numerous data checks were done at each stage. Second and sometimes third viewings of photologs, videotapes, and plans occurred, as well as consistency checks on SAS data base entries and some checks on the HSIS files themselves. Variables such as Roadside Hazard Rating were determined by two and sometimes three different individuals to minimize subjectivity.
HSIS Data
Accident data, traffic data, vertical and horizontal alignment data for Washington State, and other geometric data were extracted from HSIS files. These data were used in part to constrain the populations so that segments were on two-lane paved rural roads where segment lengths, surface widths, shoulder widths, ADT, and commercial ADT fell within prescribed ranges, while intersection geometries were three-legged or four-legged with all legs two-lane and two-way rural
roads.
The data elements for the samples are those shown in Table 1. In the case of Washington State
vertical and horizontal alignment data were obtained from HSIS files, but for Minnesota they were
obtained from construction plans.
Minnesota Photologs
Photologs for the State of Minnesota were examined at FHWA's Turner-Fairbank Highway Research
Center. In some cases photologs were not available at FHWA, but were found and examined at the Minnesota Department of Transportation (MNDOT) in Saint Paul, Minnesota. The photologs were used to verify HSIS data (e.g., rural environment, two lanes, stop sign on minor road), to determine Roadside Hazard Rating, to count driveways and intersections within a segment, to determine channelization at intersections, and to note posted regulatory and advisory speeds when seen.
Minnesota Construction Plans
Construction plans obtained in the Plan Office of MNDOT provided horizontal and vertical alignment data as well as the angle between legs at intersections. Location of plans was an arduous task, requiring that true beginning and ending mileposts of a segment or reference point of an intersection be matched up to the correct stations, that a control section be determined from a separate book, that a card file of projects by segment be consulted to discover any projects and project numbers, and then that the corresponding project plan sheets be recovered and verified. Plans were then copied and were examined in detail at a later time.
Washington Videotapes
Videotapes for the State of Washington's roadways were purchased from the Washington Department of Transportation and were reviewed at PRAGMATICS. Like the Minnesota photologs,
the videotapes were used to verify the correctness of the HSIS data and to obtain Roadside Hazard Rating, speeds, numbers of driveways, and channelization. In addition, they were used to estimate the angle between legs at an intersection.
Weather Data
Weather data were acquired for Minnesota intersections. The Midwestern Climate Center (MCC) in
Illinois provided a listing of the nine Climate Districts in Minnesota, each of which is relatively homogeneous in its weather conditions. Weather data for each District are available based on averages of reports from local weather stations, many of which are run by volunteers. In Northern Minnesota the stations are sparser than elsewhere in the State. The percentages of dry, wet, snow/slush, and ice/pack snow days, respectively, for each year from 1985 to 1989 by Climate District were provided at a nominal charge. PRAGMATICS, Inc. staff attached these to segments and intersections falling within the corresponding Climate District.
Modeling of the Minnesota data did not show the weather to be significant, possibly because
the weather variable could not be localized to a level below the Climate District. Consequently, weather data were not acquired for Washington State.
Miscellaneous Investigations
Aerial photographs were consulted in both Minnesota and Washington for possible use in estimating horizontal alignment, intersection angles, and intersection channelization. The Photogrammetric Unit of MNDOT provided contact prints for 12 out of 20 requested intersections at a scale of 1" = 100'; the other eight were not available. Washington State provided a few sample prints of aerial photographs at a scale of 1" = 2,000'. Curvatures and angles could be readily made out from the Washington photos, but channelization at intersections was not readily ascertainable. Since the information could be obtained in other ways, not all intersections and segments were available in aerial photographs, and the cost was high in Washington State, it was decided not to acquire such photos for the full samples.
Minnesota has nine Highway Districts. Each Highway District Office was queried for information about a sample of intersections (channelization installation dates, age of stop signs on minor roads). Age of stop signs is thought to be related to reflectivity and visibility. All nine Districts responded and provided some information, including sketches of the intersections. In all cases the channelization (turning and/or acceleration lanes) was installed prior to 1985, but exact installation dates were not available. Likewise the dates of stop sign installations were
not generally available, but the District Offices indicated that stop signs were replaced on a 10-year schedule.
Queries were also made in Minnesota about traffic data and commercial traffic data, as well as
the availability of traffic data on county roads, and in both Minnesota and Washington about underreporting of accidents. Results are reported below.
Table 1. Variables collected in the study
|
|
MINNESOTA SEGMENTS
|
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Identifiers
|
m_sysnbr
|
Route number
|
|
HSIS
|
|
true_beg
|
true beg. Milepost
|
miles
|
HSIS
|
|
true_end
|
true end milepost
|
miles
|
HSIS
|
|
beg_sta
|
beg. Station
|
hundreds of feet
|
Plans
|
|
end_sta
|
end station
|
hundreds of feet
|
Plans
|
|
Traffic
|
ADT
|
Average daily traffic
|
vehicles per day
|
HSIS
|
|
com_avg
|
Average daily heavy vehicle traffic
|
vehicles per day
|
HSIS
|
|
Miscellaneous
|
LW
|
lane width
|
feet
|
HSIS
|
|
SHW
|
Shoulder width
|
feet
|
HSIS
|
|
RHR
|
Roadside Hazard Rating
|
1, 2, 3, 4, 5, 6, 7
|
Photologs
|
|
nodrwy,
noint
|
Number of driveways, number of intersections
|
|
Photologs
|
|
shl_typ
|
Shoulder type
|
|
HSIS
|
|
light
|
yes or no if lighting/no lighting
|
|
Photologs
|
|
terrain
|
flat, rolling, or mountainous
|
|
Photologs
|
|
Weather
|
dd, wd, ss, ips
|
Number of dry, wet, snow/slush, ice/packsnow days
|
days per year
|
MCC
|
|
Horizontal alignment
|
pc{i}
|
beg. Station of curve no. I
|
hundreds of feet
|
Plans
|
|
pt{i}
|
end station of curve no. i
|
hundreds of feet
|
Plans
|
|
DEG{i}
|
degree of curve, curve no. I
|
degrees per 100 ft
|
Plans
|
|
dir{i}
|
Direction, left or right, curve no. i
|
|
Plans
|
|
Vertical alignment
|
b{i}
|
beg. Station of curve no. I
|
hundreds of feet
|
Plans
|
|
e{i}
|
end station of curve no. I
|
hundreds of feet
|
Plans
|
|
g{i}
|
grade no. i (prior to curve no. i)
|
percent
|
Plans
|
Variables explicitly used in models are in capital letters; 1 mi = 1.61 km, 1 ft = 0.3048 m
Table 1. Variables collected in the study (continued)
|
|
MINNESOTA SEGMENTS, continued
|
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Speed
|
advspd
|
advisory speed
|
miles per hour
|
Photologs
|
|
regspd
|
Regulatory speed
|
miles per hour
|
Photologs
|
|
speed
|
posted speed (accident sites only)
|
miles per hour
|
HSIS
|
|
Accident data
|
TOTACC
|
total number of non-intersection accidents in 1985-9, 1990-3
|
|
HSIS
|
|
fatal,
injury, nonincap,
possinj, injunk, propdam
|
no. of fatal, injury,
non-incapacitating, possible injury, injury unknown, and property damage
only non-intersection accidents
|
|
HSIS
|
|
rearend, sswipe, leftturn, rorleft, rtangle, riteturn, rorright, headon,
sswipopp, other, unknown
|
no. of rearend, sideswipe, left turn, run-off-road left, right angle,
right turn, run-off-road right, headon, sideswipe opposite, other, and
type unknown accidents
|
|
HSIS
|
Table 1. Variables collected in the study (continued)
|
|
MINNESOTA THREE-LEGGED AND FOUR-LEGGED INTERSECTIONS
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Identifiers
|
int_synb
|
Route number
|
|
HSIS
|
|
refpnt
|
nominal milepost of intersection center
|
miles
|
HSIS
|
|
true_sta
|
station of intersection center
|
hundreds of feet
|
Plans
|
|
Traffic
|
int1
|
average daily traffic on major road
|
vehicles per day
|
HSIS
|
|
int2
|
average daily traffic on minor road
|
vehicles per day
|
HSIS
|
|
Miscellaneous
|
RHRI
|
Roadside Hazard Rating within ±250 ft on major road
|
1, 2, 3, 4, 5, 6, 7
|
Photologs
|
|
ND
|
number of driveways within ±250 ft on major road
|
|
Photologs
|
|
light
|
yes or no if lighting or no lighting
|
|
Photologs
|
|
terrain
|
flat, rolling, or mountainous
|
|
Photologs
|
|
Weather
|
dd, wd, ss, ips
|
number of dry, wet, snow/slush, ice\packsnow days
|
days per year
|
MCC
|
|
Horizontal
Alignment on major road
|
pc{i}
|
beg. station of curve no. i (if any portion of curve is within ±764 ft
of intersection center along major road)
|
hundreds of feet
|
Plans
|
|
pt{i}
|
end station, curve no. i
|
hundreds of feet
|
Plans
|
|
DEG{i}
|
degree of curve, curve no. I
|
degrees per hundred feet
|
Plans
|
|
dir{i}
|
direction, left or right, curve no. I
|
|
Plans
|
|
Vertical alignment on major
Road
|
b{i}
|
beg. station of curve no. i (if any portion of curve is within ±764 ft
of intersection center along major road)
|
hundreds of feet
|
Plans
|
|
e{i}
|
end station of curve no. I
|
hundreds of feet
|
Plans
|
|
g{i}
|
grade no. i (prior to curve no. i)
|
percent
|
Plans
|
Table 1. Variables collected in the study (continued)
Table 1. Variables collected in the study (continued)
|
|
MINNESOTA THREE-LEGGED INTERSECTIONS ONLY
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Angle
|
angle
|
angle between increasing direction of major road and third leg
|
degrees
|
Plans
|
|
dir_ang
|
direction of third leg (left or right ) from increasing dir. of major road
|
|
Plans
|
|
Channelization
|
tlml
|
yes or no whether a right turn lane does or does not exist on major road
|
|
Photologs
|
|
tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the minor road
|
|
Photologs
|
|
bypass
|
yes or no whether a bypass lane does or does not exist on the major road
(opposite the minor road)
|
|
Photologs
|
|
|
MINNESOTA FOUR-LEGGED INTERSECTIONS ONLY
|
|
Angle
|
l_angle
|
angle between increasing direction of major road and left leg of minor
|
degrees
|
Plans
|
|
r_angle
|
angle between increasing direction of major road and right leg of minor
|
degrees
|
Plans
|
|
Channelization
|
tlml1
|
yes or no whether a right turn lane does or does not exist along increasing
direction of major road
|
|
Photologs
|
|
tlml2
|
yes or no whether a right turn lane does or does not exist along decreasing
direction of major road
|
|
Photologs
|
|
l_tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the left leg of the minor road
|
|
Photologs
|
|
r_tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the right leg of the minor road
|
|
Photologs
|
Table 1. Variables collected in the study (continued)
|
|
WASHINGTON SEGMENTS
|
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Identifiers
|
rte_nbr
|
Route number
|
|
HSIS
|
|
begmp
|
beg. Milepost
|
miles
|
HSIS
|
|
endmp
|
end milepost
|
miles
|
HSIS
|
|
Traffic
|
ADT
|
average daily traffic
|
vehicles per day
|
HSIS
|
|
com_avg
|
average daily heavy vehicle traffic
|
vehicles per day
|
HSIS
|
|
Miscellaneous
|
LW
|
lane width
|
feet
|
HSIS
|
|
SHW
|
shoulder width
|
feet
|
HSIS
|
|
RHR
|
Roadside Hazard Rating
|
1, 2, 3, 4, 5, 6, 7
|
Photologs
|
|
nodrwy
|
number of driveways
|
|
Photologs
|
|
noint
|
number of intersections
|
|
Photologs
|
|
light
|
yes or no if lighting or no lighting
|
|
Photologs
|
|
terrain
|
flat, rolling, or mountainous
|
|
Photologs
|
|
Horizontal alignment
|
pc{i}
|
beg. milepost of curve no. I
|
miles
|
HSIS
|
|
pt{i}
|
end milepost of curve no. i
|
miles
|
HSIS
|
|
rad{i}
|
radius of curve, curve no. I
|
feet
|
HSIS
|
|
dir{i}
|
direction, left or right, curve no. I
|
|
HSIS
|
|
Vertical alignment
|
b{i}
|
beg. milepost of curve no. I
|
miles
|
HSIS
|
|
e{i}
|
end milepost of curve no. I
|
miles
|
HSIS
|
|
g{i}
|
incoming grade no. I
|
percent
|
HSIS
|
|
h{i}
|
outgoing grade no. I
|
percent
|
HSIS
|
Table 1. Variables collected in the study (continued)
|
|
WASHINGTON SEGMENTS, continued
|
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Speed
|
advspd
|
advisory speed
|
miles per hour
|
Photologs
|
|
regspd
|
regulatory speed
|
miles per hour
|
Photologs
|
|
spd_limt
|
posted speed
|
miles per hour
|
HSIS
|
|
hspd{i}
|
speed on horizontal curve no. I
|
miles per hour
|
HSIS
|
|
vspd{i}
|
speed on vertical curve no. I
|
miles per hour
|
HSIS
|
|
Accident data
|
TOTACC
|
total number of non-intersection accidents in 1993-5
|
|
HSIS
|
|
fatal,
injury, nonincap,
possinj, injunk, propdam
|
no. of fatal, injury,
non-incapacitating, possible injury, injury unknown, and property damage
only non-intersection accidents
|
|
HSIS
|
|
RORACC
|
number of run-off-road accidents
|
|
HSIS
|
Table 1. Variables collected in the study (continued)
|
|
WASHINGTON THREE-LEGGED AND FOUR-LEGGED INTERSECTIONS
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Identifiers
|
rte_nbr
|
Route number
|
|
HSIS
|
|
arm
|
accumulated milepost of intersection center
|
miles
|
HSIS
|
|
Traffic
|
ADT1
|
average daily traffic on major road
|
vehicles per day
|
HSIS
|
|
ADT2
|
average daily traffic on minor road
|
vehicles per day
|
HSIS
|
|
Miscellaneous
|
RHRI
|
Roadside Hazard Rating within ±250 ft on major road
|
1, 2, 3, 4, 5, 6, 7
|
Photologs
|
|
ND
|
number of driveways within ±250 ft on major road
|
|
Photologs
|
|
light
|
yes or no if lighting or no lighting
|
|
Photologs
|
|
terrain
|
flat, rolling, or mountainous
|
|
Photologs
|
|
Horizontal
Alignment on major road
|
pc{i}
|
beg. milepost of horizontal curve no. i (if any portion of curve is within
±764 ft of intersection center along major road)
|
miles
|
HSIS
|
|
pt{i}
|
end milepost, curve no. i
|
miles
|
HSIS
|
|
rad{i}
|
radius of curve, curve no. I
|
feet
|
HSIS
|
|
dir{i}
|
direction, left or right, curve no. I
|
|
HSIS
|
|
Vertical alignment on major
Road
|
b{i}
|
beg. milepost of vertical curve no. i (if any portion of curve is within
±764 ft of intersection center along major road)
|
miles
|
HSIS
|
|
e{i}
|
end milepost of vertical curve no. i
|
miles
|
HSIS
|
|
g{i}
|
grade no. I
|
percent
|
HSIS
|
Table 1. Variables collected in the study (continued)
|
|
WASHINGTON THREE-LEGGED AND FOUR-LEGGED INTERSECTION, continued
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Speed on major road
|
advspd
|
advisory speed
|
miles per hour
|
Photologs
|
|
regspd
|
regulatory speed
|
miles per hour
|
Photologs
|
|
ap_spd
|
posted approach speed
|
miles per hour
|
HSIS
|
|
Accident data
|
TOTACC
|
number of intersection accidents or intersection-related accidents occurring
within ±250 feet of intersection on major road during 1985-9, 1990-3
|
|
HSIS
|
|
fatal, injury, nonincap,
possinj, injunk, propdam
|
no. of fatal, injury,
non-incapacitating, possible injury, injury unknown, and property damage
only accidents
|
|
HSIS
|
|
rearend, sswipe, leftturn, rorleft, rtangle, riteturn, rorright, headon,
sswipopp, other, unknown
|
no. of rearend, sideswipe, left turn, run-off-road left, right angle,
right turn, run-off-road right, headon, sideswipe opposite, other, and
type unknown accidents
|
|
HSIS
|
|
RORACC
|
number of run-off-road accidents
|
|
HSIS
|
Table 1. Variables collected in the study (continued)
|
|
WASHINGTON THREE-LEGGED INTERSECTIONS ONLY
|
|
Variable
|
Meaning
|
Units
|
Source
|
|
Angle
|
angle
|
angle between increasing direction of major road and third leg
|
degrees
|
Photologs
|
|
dir_ang
|
direction of third leg (left or right ) from increasing dir. of major
road
|
|
Photologs
|
|
Channelization
|
tlml
|
yes or no whether a right turn lane does or does not exist on major road
|
|
Photologs
|
|
tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the minor road
|
|
Photologs
|
|
bypass
|
yes or no whether a bypass lane does or does not exist on the major road
(opposite the minor road)
|
|
Photologs
|
|
|
WASHINGTON FOUR-LEGGED INTERSECTIONS ONLY
|
|
Angle
|
l_angle
|
angle between increasing direction of major road and left leg of minor
|
degrees
|
Photologs
|
|
r_angle
|
angle between increasing direction of major road and right leg of minor
|
degrees
|
Photologs
|
|
Channelization
|
tlml1
|
yes or no whether a right turn lane does or does not exist along increasing
direction of major road
|
|
Photologs
|
|
tlml2
|
yes or no whether a right turn lane does or does not exist along decreasing
direction of major road
|
|
Photologs
|
|
l_tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the left leg of the minor road
|
|
Photologs
|
|
r_tlcs
|
yes or no whether a right turn/acceleration lane does or does not exist
on the right leg of the minor road
|
|
Photologs
|
|
